Large commercial jet airplanes typically include two main landing gear assemblies that are attached to the undersides of the wings near the fuselage. When deployed, the landing gear assemblies extend downwardly for supporting the airplane during landings and taxiing. When retracted, the landing gear assemblies are stowed in a wheel well in the airplane fuselage. During normal airplane operations, the landing gear assemblies are subject to several types of mechanical load. For example, when the airplane is stationary or slowing taxiing, the landing gear assemblies must withstand the static weight load of the airplane. The main landing gear assemblies are additionally subjected to large, vertical loads when the airplane touches down on the runway. Large, rearwardly directed drag loads can also be present at touchdown and when the brakes are applied. Further, during steering maneuvers, the landing gear assemblies are subjected to side loads. All of these various loading conditions are reacted by the components of the landing gear and, ultimately, by the landing gear support structures that attach the gear to the airplane. Thus, a considerable amount of design and development effort has been directed to providing landing gear assemblies in which the landing gear load path geometry distributes the loads between the wing and fuselage of the airplane.
One design that has been used to successfully spread the loads between the airplane wing and fuselage uses four discrete attachment points for joining the landing gear assembly to the airplane. Although the use of four attachment points has been successfully used to distribute load in airplanes (such as the Boeing models 767 and 777), the arrangement is subject to a disadvantage and drawback. In particular, because four attachment points are used, the internal loads and attachment loads are statically indeterminate. Thus, the load distribution between the airplane wing and fuselage is a function of the stiffness of the members that join the landing gear to the wing and fuselage. As a result, designing and developing four-point landing gear attachment arrangements can present difficult tasks. In particular, during the design and development of an airplane, changes may be required that may effect the stiffness of the structure used to attach the landing gear to the four attachment points of the airplane. To accommodate these changes, it may be necessary to make changes in the four-point attachment arrangement that add additional weight or, in an extreme case, a redesign could be required.
A further design consideration is that the main landing gear of large commercial airplanes is designed to breakaway from the airplane under severe overload conditions, such as off-runway excursions, high sink rate landings, etc., so that the gear will not break open fuel tanks that are contained in the wings. In some arrangements, the trunnion attachment used to join the landing gear with the airplane is very stiff as a result of a cantilever trunnion support. In such an arrangement, the trunnions typically carry very high loads, thus requiring that the trunnion pins be high strength fuse links in order to achieve landing gear breakaway. The very large design loads that result from the use of high-strength fuse pins can present disadvantages with respect to the necessary size of the airplane wing box.